//
// execution/schedule.hpp
// ~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_EXECUTION_SCHEDULE_HPP
#define ASIO_EXECUTION_SCHEDULE_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"
#include "asio/detail/type_traits.hpp"
#include "asio/execution/executor.hpp"
#include "asio/traits/schedule_member.hpp"
#include "asio/traits/schedule_free.hpp"

#include "asio/detail/push_options.hpp"

#if defined(GENERATING_DOCUMENTATION)

namespace asio {
namespace execution {

/// A customisation point that is used to obtain a sender from a scheduler.
/**
 * The name <tt>execution::schedule</tt> denotes a customisation point object.
 * For some subexpression <tt>s</tt>, let <tt>S</tt> be a type such that
 * <tt>decltype((s))</tt> is <tt>S</tt>. The expression
 * <tt>execution::schedule(s)</tt> is expression-equivalent to:
 *
 * @li <tt>s.schedule()</tt>, if that expression is valid and its type models
 *   <tt>sender</tt>.
 *
 * @li Otherwise, <tt>schedule(s)</tt>, if that expression is valid and its
 *   type models <tt>sender</tt> with overload resolution performed in a context
 *   that includes the declaration <tt>void schedule();</tt> and that does not
 *   include a declaration of <tt>execution::schedule</tt>.
 *
 * @li Otherwise, <tt>S</tt> if <tt>S</tt> satisfies <tt>executor</tt>.
 *
 * @li Otherwise, <tt>execution::schedule(s)</tt> is ill-formed.
 */
inline constexpr unspecified schedule = unspecified;

/// A type trait that determines whether a @c schedule expression is
/// well-formed.
/**
 * Class template @c can_schedule is a trait that is derived from @c true_type
 * if the expression <tt>execution::schedule(std::declval<S>())</tt> is well
 * formed; otherwise @c false_type.
 */
template <typename S>
struct can_schedule :
  integral_constant<bool, automatically_determined>
{
};

} // namespace execution
} // namespace asio

#else // defined(GENERATING_DOCUMENTATION)

namespace asio_execution_schedule_fn {

    using asio::decay;
    using asio::declval;
    using asio::enable_if;
    using asio::execution::is_executor;
    using asio::traits::schedule_free;
    using asio::traits::schedule_member;

    void schedule();

    enum overload_type {
        identity,
        call_member,
        call_free,
        ill_formed
    };

    template<typename S, typename = void, typename = void, typename = void>
    struct call_traits {
        ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed
        );

        ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);

        typedef void result_type;
    };

    template<typename S>
    struct call_traits<S,
            typename enable_if<
                    schedule_member<S>::is_valid
            >::type> :
            schedule_member<S> {
        ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
    };

    template<typename S>
    struct call_traits<S,
            typename enable_if<
                    !schedule_member<S>::is_valid
            >::type,
            typename enable_if<
                    schedule_free<S>::is_valid
            >::type> :
            schedule_free<S> {
        ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
    };

    template<typename S>
    struct call_traits<S,
            typename enable_if<
                    !schedule_member<S>::is_valid
            >::type,
            typename enable_if<
                    !schedule_free<S>::is_valid
            >::type,
            typename enable_if<
                    is_executor<typename decay<S>::type>::value
            >::type> {
        ASIO_STATIC_CONSTEXPR(overload_type, overload = identity
        );

        ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);

#if defined(ASIO_HAS_MOVE)
        typedef ASIO_MOVE_ARG(S) result_type;
#else // defined(ASIO_HAS_MOVE)
        typedef ASIO_MOVE_ARG(
        typename decay<S>::type)
        result_type;
#endif // defined(ASIO_HAS_MOVE)
    };

    struct impl {
        template<typename S>
        ASIO_CONSTEXPR typename enable_if<
                call_traits<S>::overload == identity,
                typename call_traits<S>::result_type
        >::type

        operator()(ASIO_MOVE_ARG(S) s) const

        ASIO_NOEXCEPT_IF((
                call_traits<S>::is_noexcept))
                {
                        return ASIO_MOVE_CAST(S)(s);
                }

#if defined(ASIO_HAS_MOVE)
        template <typename S>
        ASIO_CONSTEXPR typename enable_if<
          call_traits<S>::overload == call_member,
          typename call_traits<S>::result_type
        >::type
        operator()(S&& s) const
          ASIO_NOEXCEPT_IF((
            call_traits<S>::is_noexcept))
        {
          return ASIO_MOVE_CAST(S)(s).schedule();
        }

        template <typename S>
        ASIO_CONSTEXPR typename enable_if<
          call_traits<S>::overload == call_free,
          typename call_traits<S>::result_type
        >::type
        operator()(S&& s) const
          ASIO_NOEXCEPT_IF((
            call_traits<S>::is_noexcept))
        {
          return schedule(ASIO_MOVE_CAST(S)(s));
        }
#else // defined(ASIO_HAS_MOVE)
        template<typename S>
        ASIO_CONSTEXPR typename enable_if<
                call_traits<S &>::overload == call_member,
                typename call_traits<S &>::result_type
        >::type

        operator()(S &s) const

        ASIO_NOEXCEPT_IF((
                call_traits<S &>::is_noexcept))
                {
                        return s.schedule();
                }

        template<typename S>
        ASIO_CONSTEXPR typename enable_if<
                call_traits<const S &>::overload == call_member,
                typename call_traits<const S &>::result_type
        >::type

        operator()(const S &s) const

        ASIO_NOEXCEPT_IF((
                call_traits<const S &>::is_noexcept))
                {
                        return s.schedule();
                }

        template<typename S>
        ASIO_CONSTEXPR typename enable_if<
                call_traits<S &>::overload == call_free,
                typename call_traits<S &>::result_type
        >::type

        operator()(S &s) const

        ASIO_NOEXCEPT_IF((
                call_traits<S &>::is_noexcept))
                {
                        return schedule(s);
                }

        template<typename S>
        ASIO_CONSTEXPR typename enable_if<
                call_traits<const S &>::overload == call_free,
                typename call_traits<const S &>::result_type
        >::type

        operator()(const S &s) const

        ASIO_NOEXCEPT_IF((
                call_traits<const S &>::is_noexcept))
                {
                        return schedule(s);
                }
#endif // defined(ASIO_HAS_MOVE)
    };

    template<typename T = impl>
    struct static_instance {
        static const T instance;
    };

    template<typename T>
    const T static_instance<T>::instance = {};

} // namespace asio_execution_schedule_fn
namespace asio {
    namespace execution {
        namespace {

            static ASIO_CONSTEXPR const asio_execution_schedule_fn::impl
            &
            schedule = asio_execution_schedule_fn::static_instance<>::instance;

        } // namespace

        template<typename S>
        struct can_schedule :
                integral_constant<bool,
                        asio_execution_schedule_fn::call_traits<S>::overload !=
                        asio_execution_schedule_fn::ill_formed> {
        };

#if defined(ASIO_HAS_VARIABLE_TEMPLATES)

        template <typename S>
        constexpr bool can_schedule_v = can_schedule<S>::value;

#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)

        template<typename S>
        struct is_nothrow_schedule :
                integral_constant<bool,
                        asio_execution_schedule_fn::call_traits<S>::is_noexcept> {
        };

#if defined(ASIO_HAS_VARIABLE_TEMPLATES)

        template <typename S>
        constexpr bool is_nothrow_schedule_v
          = is_nothrow_schedule<S>::value;

#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)

    } // namespace execution
} // namespace asio

#endif // defined(GENERATING_DOCUMENTATION)

#include "asio/detail/pop_options.hpp"

#endif // ASIO_EXECUTION_SCHEDULE_HPP
